The comments are not the problem; if they bother, give the reader a button to show or hide them. Better still, the comments bring some “intelligence” to the community: an article with a comment, even if it just says “good job...”, is somehow better than an article without any comment. Furthermore the comments are used to sort articles to ease some type of lectures…

The articles are public and anybody can give his opinion about them, this is the essence of a social networking.
So the problem is not there in the comments, the problem is with the articles themselves; how to improve their quality?

Note that any solution to this problem must take into consideration at least the following constraints:

Yii community is not a scientific organization, it is a social network.

Heterogeneous level of understanding the framework, the language php, …

I agree with abajja! Many times comments add very interesting views as well as providing additional information about the article itself. It just does NOT make sense to display a maximum of 20 comments only and leave the rest hiding in database forever. There's plenty of articles where it would be quite useful to see older comments. Otherwise newer members of the community continue asking the very same questions (that had already been answered before) over and over again just because they can't see the oldest comments and potential answers anymore.

It's not such a big deal to add a "show more comments" ajax link at the bottom of the list, and/or add a link to an extra page to "show all comments" at once; or have tabs to show newest, oldest, best rated comments.

The idea of a wiki is to edit the article itself... comments can be used to make a discussion about the main idea... but if something is important to the article itself it should be added to the article.. anybody can edit anyones wiki... that's the main point of a wiki itself.